1. Field of the invention
The present invention relates to an electroluminescence (EL) element having an EL layer made of an emitting substance, which utilizes electroluminescence phenomenon that the emitting substance emits light by applying an electric current to the EL layer. More particularly, it is concerned with an organic electroluminescence element (organic EL element) in which the EL layer is made of an organic emitting substance.
2. Description of the prior art
As prior art organic EL elements, there have been known an element of two-layer structure having two layers of organic compounds as shown in FIG. 1, in which an organic fluorescent thin film 3 (hereinafter referred as "EL layer") and an organic hole transport layer 4 are laminated with each other and are arranged between a metal cathode 1 and a transparent anode 2. There have been also known an element of three-layer structure having three layers of organic compounds as shown in FIG. 2, in which an organic electron transport layer 5, an EL layer and an organic hole transport layer 4 are laminated in sequence and are sandwiched as a whole between a metal cathode 1 and a transparent anode 2. The hole transport layer 4 facilitates the infusion of the holes from the anode and blocks electrons. The electron transport layer 5 facilitates the infusion of electrons from the cathode.
In these organic EL elements, a glass substrate 6 is furnished outside the transparent anode 2. The recombination of electrons infused from the metal cathode 1 and the holes infused from the transparent anode 2 to the EL layer 3 generates excitons. The excitons emit light when they are deactivated through radiation. This light radiates toward outside through the transparent anode 2 and the glass substrate 6 (See Japanese Patent Patent Laid-opens Nos.59-194393 and 63-295695).
The conventional organic EL elements constructed as indicated above generally emit light even at a low voltage. However, when the EL element formed with a simple matrix structure of electrode strips is continuously driven by a DC voltage, a leakage current occurs in a cross portion of the electrode strips. As a result, the portion not to emit light, i.e. the periphery of the cross portion, may emit light, and/or such an EL element easily becomes destructible. Further, there are strong demands on an organic EL element emitting light at a high luminance in the industrial market.